1. Field of the Invention
The present invention relates to a circular polarization filter. In addition, the present invention relates to the application of a circular polarization filter to a light source, a sensor, a sensor system, or the like.
2. Description of the Related Art
Circular polarization filters are filters capable of selectively transmitting or reflecting either right-handed circularly polarized light or left-handed circularly polarized light in a specific wavelength region, and are applied in various fields by utilizing characteristics of the obtained circularly polarized light.
For example, WO2012/144422A discloses usage of circularly polarized light in plant cultivation, and using a circular polarization plate in a lighting device for plant cultivation is described therein.
JP2013-36888A discloses an inspection system using circularly polarized light. JP2013-36888A discloses a technology of detecting cracks of a silicon substrate using a system which irradiates the silicon substrate with circularly polarized infrared light via a circular polarization filter and receives reflected or transmitted light from the silicon substrate via the circular polarization filter. This technology uses the fact that reflected or transmitted light from a portion having no cracks is circularly polarized light of the opposite sense and cannot be transmitted through the circular polarization filter, but in the case of reflected or transmitted light from a crack, light which can be detected via the circular polarization filter by diffuse reflection is generated.